typedef struct my_custom_pbuf {
    struct pbuf_custom p;
    void* dma_descriptor;
} my_custom_pbuf_t;

LWIP_MEMPOOL_DECLARE(RX_POOL, 10, sizeof(my_custom_pbuf_t), "Zero-copy RX PBUF pool");

void my_pbuf_free_custom(void* p)
{
    SYS_ARCH_DECL_PROTECT(old_level);

    my_custom_pbuf_t* my_puf = (my_custom_pbuf_t*)p;

    // invalidate data cache here - lwIP and/or application may have written into buffer!
    // (invalidate is faster than flushing, and noone needs the correct data in the buffer)
    invalidate_cpu_cache(p->payload, p->tot_len);

    SYS_ARCH_PROTECT(old_level);
    free_rx_dma_descriptor(my_pbuf->dma_descriptor);
    LWIP_MEMPOOL_FREE(RX_POOL, my_pbuf);
    SYS_ARCH_UNPROTECT(old_level);
}

void eth_rx_irq()
{
    dma_descriptor*   dma_desc = get_RX_DMA_descriptor_from_ethernet();
    my_custom_pbuf_t* my_pbuf  = (my_custom_pbuf_t*)LWIP_MEMPOOL_ALLOC(RX_POOL);

    my_pbuf->p.custom_free_function = my_pbuf_free_custom;
    my_pbuf->dma_descriptor         = dma_desc;

    invalidate_cpu_cache(dma_desc->rx_data, dma_desc->rx_length);

    struct pbuf* p = pbuf_alloced_custom(PBUF_RAW,
                                         dma_desc->rx_length,
                                         PBUF_REF,
                                         &my_pbuf->p,
                                         dma_desc->rx_data,
                                         dma_desc->max_buffer_size);

    if(netif->input(p, netif) != ERR_OK) {
        pbuf_free(p);
    }
}
